The headlight for a car includes a high beam and a low beam, and a driver may select to use one of them or switch between them depending on actual road conditions. It is also known as a polite and safety measure in driving to switch high beam to low beam when meeting with an opposite coming car or getting close to a front car moving in the same direction. Generally, it is proper for a driver to switch from high beam to low beam when a distance from an opposite coming car is about 20 to 30 meters, or when a distance from a front car is about 1 to 3 meters, lest the driver of the opposite or the front car should be dangerously dazzled by the strong light projected toward him or a rearview mirror in the car, respectively. Up to date, most of the known dip switches are manually operated and a large number of drivers fail to timely operate the manual dip switch to effectively switch the headlight between high and low beams due to the driver's personal habit or negligence in driving. Moreover, repeated operation of the manual dip switch will inevitably bring inconvenience and confusion to the driver and even endanger the driver's safety in driving.